Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity - Additional Information (Detail)

v3.19.2
Stockholders' Equity - Additional Information (Detail) - USD ($)
3 Months Ended 6 Months Ended 12 Months Ended
Feb. 25, 2019
Jun. 30, 2019
Mar. 31, 2019
Jun. 30, 2018
Mar. 31, 2018
Jun. 30, 2019
Jun. 30, 2018
Dec. 31, 2017
Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Authorized capital stock   520,000,000       520,000,000      
Common stock, par value   $ 0.0001       $ 0.0001     $ 0.0001
Common stock, shares authorized   500,000,000       500,000,000     500,000,000
Preferred stock, par value   $ 0.0001       $ 0.0001      
Preferred stock, shares authorized   20,000,000       20,000,000      
Preferred stock, shares outstanding   0       0     0
Proceeds from sale of common stock, net           $ 7,630,000 $ 47,586,000    
Stock option granted description terms           the exercise price of an option granted to a 10% shareholder cannot be less than 110% of the estimated fair value of the shares on the date of grant. Options granted generally vest over four years and expire in seven to ten years.      
Ownership percent           10.00%      
Shares of common stock, reserved for issuance   14,536,178       14,536,178      
Common stock, shares exercised           181,664 622,982    
Option intrinsic value, exercised           $ 3,300,000 $ 11,300,000    
Net tax benefits related to exercised options           0      
Stock purchase, value   $ 1,802,000 $ 2,898,000 $ 8,661,000 $ 6,196,000        
Stock-based compensation expense   $ 15,201,000   $ 7,998,000   $ 27,470,000 15,013,000    
2014 Equity Incentive Plan                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Shares of common stock, reserved for issuance   12,135,316       12,135,316      
Aggregate number of awards available for grant to be issued   7,893,825       7,893,825      
Outstanding options and RSUs   4,241,491       4,241,491      
Inducement Plan                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Shares of common stock, reserved for issuance   1,223,621       1,223,621      
Aggregate number of awards available for grant to be issued   404,172       404,172      
Outstanding options and RSUs   819,449       819,449      
2014 Employee Stock Purchase Plan                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Percentage of employees purchase price of common stock           85.00%      
Shares of common stock, reserved for issuance   1,067,575       1,067,575      
Unrecognized stock-based compensation expense   $ 1,400,000       $ 1,400,000      
Employee stock purchase plan description           (i) the beginning of a 12-month offering period, or (ii) at the end of one of the two related 6-month purchase periods      
Stock-based compensation expense           $ 500,000 $ 200,000    
Shares purchased           74,439 77,100    
Aggregate number of shares authorized   1,355,973       1,355,973      
Restricted Stock Units (RSUs)                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Weighted average grant date fair value per share           $ 35.17 $ 36.69    
Unrecognized stock-based compensation expense   $ 44,600,000       $ 44,600,000      
Unrecognized stock-based compensation weighted average recognition period           2 years 10 months 24 days      
Aggregate intrinsic value   30,800,000       $ 30,800,000      
Restricted stock units, settled           528,589 380,034    
RSU settlements, net of shares withheld, shares           482,714 233,836    
Restricted stock units withheld for tax obligations           210,865 87,954    
Restricted stock units withheld for tax obligations, value           $ 6,700,000 $ 3,400,000    
Restricted Stock Units (RSUs) | From Date Of Grant                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Share based compensation, vesting period           4 years      
Restricted Stock Units (RSUs) | Following Service Termination Date                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Share based compensation award expiration period           2 years      
Employees And Non Employees                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Share based compensation, vesting period           4 years      
Vested and Unvested Options                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Unrecognized stock-based compensation weighted average recognition period           2 years 10 months 24 days      
Stock options, issued               275,000  
Unrecognized stock-based compensation   $ 82,900,000       $ 82,900,000      
Maximum | 2014 Employee Stock Purchase Plan                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Stock purchase, value           $ 25,000      
Annual increase in EIP/ESPP, subject to other limitations           1.00%      
Maximum increase in number of shares available for issuance           230,769      
Maximum | Restricted Stock Units (RSUs) | From Date Of Grant                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Share based compensation award expiration period           10 years      
Maximum | Employees And Non Employees                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Share based compensation award expiration period           10 years      
Minimum                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Percentage of employees purchase price of common stock           100.00%      
Minimum | 10% Shareholder                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Percentage of employees purchase price of common stock           110.00%      
Minimum | Restricted Stock Units (RSUs) | From Date Of Grant                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Share based compensation award expiration period           7 years      
Minimum | Employees And Non Employees                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Share based compensation award expiration period           7 years      
At The Market Offering | Cowen                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Common stock, shares issued   359,234       359,234      
Common stock average price   $ 22.18       $ 22.18      
Proceeds from sale of common stock, gross   $ 8,000,000.0       $ 8,000,000.0      
Proceeds from sale of common stock, net   7,600,000       7,600,000      
Common stock value remaining to be sold   $ 92,000,000.0       $ 92,000,000.0      
At The Market Offering | Cowen | Maximum                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Common stock aggregate offering price $ 100,000,000.0                
Percentage of commission to be paid on gross sales proceeds of common stock sold 3.00%